Head and neck squamous cell carcinoma is an aggressive epithelial malignancy that has a poor five-year survival. This is due, in part, to the development of multiple primary tumors throughout the mucosa of these patients. Therefore, the use of chemopreventive strategies must be included to completely treat this disease. Retinoic acid has been the most successful chemopreventive agent against the development of new squamous cell carcinomas. The mechanisms by which retinoic acid works in a chemopreventive setting remain unclear. Recent work by this lab suggests that retinoic acid's chemopreventive effects may be partly due to its ability to make endothelial cells refractory to the inducers of angiogenesis. However, the specific molecular mechanism by which endothelial cells become refractory is unknown. The hypothesis underlying this work is that one or more members of the retinoic acid receptor (RAR) family directly participate in rendering endothelial cells refractory to inducers of angiogenesis. The goal is to determine which RARs are responsible for causing this altered response of endothelial cells. This investigator proposes to carefully determine the profile of functional RARs expressed in endothelial cells, using both Northern and Western blots, as well as electromobility shift assays (EMSA). Receptor specific ligands will then be used in in vitro and in vivo angiogenesis assays to determine which subset of expressed receptors are required for altering the ability of endothelial cells to respond to inducers of angiogenesis. Finally, the Principal Investigator proposes to transduce human microvascular endothelial cells with retroviral vectors containing either dominant negative, wild type, or chimeric RARs. These cells will then be tested in vitro for their ability to migrate towards various angiogenic substances as well as purified angiogenic factors in the presence or absence of various retinoid compounds. The transduced cells will also be implanted into mice and their ability to incorporate into newly forming blood vessels in vivo in the presence or absence of retinoids determined. These studies should advance our understanding of the biologic and molecular mechanisms by which one can modify the angiogenic response which plays a critical role in a large array of both pathologic and physiologic conditions, including the development of new primary oral squamous cell carcinomas.